PGFM (PPG Glass Filter Media) is a high-quality glass filter medium produced by Dryden Aqua. It outperforms sand and resists biological growth. PGFM is not subjected to the patented activation process and is made from mixed glass without sorting white glass. Therefore, it is not bio-resistant like AFM® ng (Activated Filter Media). AFM® ng provides superior performance and bio-resistance, while PGFM is a cheaper option for customers seeking better filter performance than sand but not wanting to invest in AFM® ng.